1. Field of the Invention
This invention relates to a medical diagnostic system and method for radiation imaging and particularly to a novel control circuit for a mechanical scanner used in the system.
2. Description of the Prior Art
The utility of directing penetrative radiation, such as X-rays, through a subject and recording the pattern of this energy emerging from the subject is well known. In the field of medical diagnosis, for example, observation of the pattern of X-rays passing through a subject frequently yields valuable information as to the condition of the subject.
In certain medical applications, radiopaque material is injected into or ingested by the subject and X-rays are then directed through the subject. The accumulation or movement of such material in or about various portions of the body can be observed by noting the pattern of X-rays emerging from the body.
One X-ray imaging system includes apparatus for producing both film camera photographs and apparently continuous television images of a subject, derived from patterns of penetrative radiation from the subject. Such a system includes a radiation source for directing radiation through the subject, and an image tube for receiving the radiation after passage through the subject and converting the radiation to a visible light image at an output, the visible image representing a pattern of the received radiation. The apparatus further includes a film camera for producing photographs of the visible output image and a television imaging system for producing a substantially continuous image representing the radiation pattern from the subject. An optical diverter apparatus is also provided for the selective transmission of the output image from the image tube to one of the television imaging system and the film camera. A collimating lens is interposed between the image tube output and the diverter, and a focusing lens is located between the diverter and the television imaging system.
In this prior system the film camera images have resolution superior to that of the television images. Thus, in regions of particular interest, when higher resolution was desired, the examiner relied on the higher resolution images produced by the film camera.
While this prior system performs well in many applications, there has still been a desire for improved performance. There has been a continuing desire for even better resolution. The necessiety for mounting the film camera, television imaging system components and diverter at predetermined locations to receive the output of the image tube makes the examining apparatus somewhat more cumbersome than is desired. Since the apparatus must be positioned and/or moved among various locations relative to the subject, this bulk of the system can cause inconvenience.
The nonlaser light used to produce the image in the prior system exhibits undesirable diffusion when optically processed, limiting system resolution. Noise in the television signal also impairs resolution. Optical losses occur because the collimating and focusing lenses must be separated by the diverter. The image power from the image tube is insufficient to expose rapidly enough newer types of fine grain film whose use can improve resolution.
Some types of light energy used to form images (e.g., laser light) can be processed to enhance the quality and resolution of these images. For example, a technique known as "apodization" can be used to enhance contrast, or the "modulation transfer function" of some images, or to emphasize either coarse or fine detail. The spatially incoherent light image from the image tube output, however, is not susceptible of enhancement of resolution or utility in this fashion. Techniques of apodization are explained in an article in the Journal of the Optical Society of America, September, 1973, Vol. 63, pp. 1071 et. seq.
The visible light from the image tube output is inherently incapable of fully retaining its resolution when optically processed. This is due in part to a phenomenon called "veiling glare." The polychromatic visible light, containing rays of differing wave length and phase, and which respond differently in refraction, is scattered when it traverses an interface between two media having differing indices of refraction, and is reflected within optical elements, such as lenses, to emerge at points distant from their expected optical paths.
The prior art system cannot take advantage of easy processability which is available in some recently-developed types of film. These films include dry-process silvered and nonsilvered (vesicular) film. The reason these new films are not applicable with the prior art system is that the output of the image tube does not possess sufficient image power (brightness) to expose these types of film as rapidly as necessary for fast exposures. The rapid exposures are needed for stopping action and for producing apparently continuous cinematic images. These objectives often require 105 millimeter exposures in as short as 1/30th of a second.
The image power needed to expose ordinary wet process, and dry process films (silvered and nonsilvered) varies greatly. For example, to expose an image 105 millimeters in diameter in 1/30th of a second on a typical wet process, fine grain film requires 1-2 milliwatts of power in the light falling on the film. By contrast, to make the same exposure on dry process silvered film requires about 30 milliwatts, while dry process nonsilvered film requires about 300-500 milliwatts. Power in the neighborhood of 30 milliwatts or greater cannot be obtained from the output phosphor light image of any presently known image tube.
In the prior system, the film camera, television camera and diverter must be mechanically coupled with respect to the image tube to maintain the film camera and television imaging components optically couplable to the image tube output. This agglomeration of equipment constitutes a bulky and heavy unit. Since the unit sometimes must be moved among various positions with respect to a subject, the unit requires complex and expensive support and counterweighting equipment for accomplishing this motion. Such equipment requires unduly large examining room space. The presence of such a large unit can add to the anxiety patients often feel during examination.
The prior system lacks flexibility in the presentation of its higher resolution film camera images. To view them, an attendant or physician must enter the examination room, remove the film from the camera and process it, a time-consuming procedure.
It is a primary object of this invention to provide a system and method for producing high energy and resolution medical diagnostic images from penetrative radiation patterns.